Railway-signal.



No.-891,339. PATENTED JUNE 23, 1908.

. RHIRT.

RAILWAY SIGNAL.

\ APPLICATION IILEDDEG. 11, 1907.

Witnesses. I Inventori- 3 4,0 by Ma UNITED STATES PATENT OFFICE.

FRANZ HIRT, OF BERLIN, GERMANY, ASSIGNOR T0 GENERAL ELECTRIC COMPANY, A

. CORPORATION OF NEW- YORK. -r

To all whom it may concern: 1

Be it known that I, FRANZ IILRT, a subject of the Emperor of Germany,.residingat Berlin, Germany, have invented certain new and useful Imrovements in Railway-Rignals, of which t 1e following is aspecification. My invention relates to railway signals, the control ofwhich is secured by the coo eration of selenium cells placed along t 1etrack and sources of light on the cars. The resistance of a seleniumcell varies with the amount of light to which the cell is exposed, as iswell known in the art, and this characteristic may be utilized tocontrol a signal by lacing a selenium cell close to the track andproviding means on the car for throwing light on the cell in passing.

A signal system thus arranged is subject, to a certain extent, todisturbances produced by variations in the light falling on the cellfrom other sources than that of a passing car. For instance, thevariation of sunlight during the day may exercise a disturbing influenceon the cell and the devices in c1r-' tem arranged in accordance with myinvention.

In the drawing A represents a car or other vehicle carrying a source ofpolarized light B. The polarization may be produced in any well known,manner. As the car passes, the light is caught by a reflector C anddirected through a lens D on the Niools prism or other double-refractingbody E. The effect of a Nicols prism on polarized light is, as is wellknown, to retract unpolarized light in two sets of rays. In the paths ofSpecification of Letters Patent. 7 Application filed December 11, 1907.Serial No. 406,030.

Iigtented June 23, 1908.

these two sets of rays are placed the two selenium cells F F in circuitwith the battery opposing windings of a differential relay I l, whichcontrols the circuit of-a suitable source of current l and thesignal-operating mechanism indicated 'diagrammatically at J.

If the light from the source B were un )olarized, or-if light from thesun, or any other source, were to fall on the reflector its rays wouldbe thrown in approximately equal proportions on the two cellsl F, sothat the currents in the opposing windings of the differential relay 11would neutralize each other but if" the light thrown from the source Bis polarized, then only one set of rays is refracted from the prism E,so that light is thrown on only one selenium cell. This produces adifference in the resistances of the two cells, resulting in anunbalancing ofthe currents in the opposing windings of the differentialrelay II, which is consequently energized, and responds to control thesignal.

I do not desire to limit myself to the particular construction andarrangement of parts here shown, but aim in the a pended claims to coverall modifications w nch are within the scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is,--

light on said controlling means.

2. In a railway signaling system, a source of polarized light carried bya vehicle, and signal controlling means responsive only to polarizedlight.

3. In a railway signaling system, a double refracting body, a pair ofdevices that vary in electric resistance with variation in light exosedrespectively to the two sets of rays relracted from said body, electrt-magnetic signal-controlling means responsive to a dinerence in theresistances of said devices, and means carried by a vehicle throwingpolarized light on said body.

4. In a railway signaling system, a doubleretracting body, a pair ofselenium cells exposed respectively tothe two sets of rays re- In serieswiththe cells are placed the fracted from said body, opposin magnet myhand this twenty-sixth day of November wincliings in] circuit withsaideels fies ic- 1907. tive ,si na -0 eratin means contro e r theiffei'iantial action of said windings, sun V FRANL I 5 means carried bya vehicle for throwing po- Witnesses:

larized light on said bod JULIUS RUMLAND, In witness whereof, havehereunto set KARL GRIEKEBEIg.

